#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() {
    ll n, k, x, y;
    cin >> n >> k >> x >> y;
    ll a[n];
    rep(i,n){
        cin >> a[i];
        a[i]--;
        if(a[i] > 0){
            a[i] = (a[i] - 1) / k + 1;
        }
    }
    sort(a,a+n,greater<ll>());

    ll ans = 0;

    if(y <= x){
        ans = a[0] * y;
    }else{
        ll now = 0;
        drep(i,n){
            if(a[i] == now){
                continue;
            }
            if(x * (i+1) > y){
                ans += y * (a[i] - now);
            }else{
                ans += x * (i+1) * (a[i] - now);
            }
            now = a[i];
        }
    }

    cout << ans << endl;
    return 0;
}